To me the only clearly constitutional compact is one that allocates the electors from the compact to winner of the vote within the compact. However, even if the compact has 270 EV, the result could be that the compact winner is not the national popular vote winner. That defeats the whole purpose of the NPVIC.
I actually think it would be interesting if non-swing states made compacts amongst themselves to pool their electoral votes. For example, if California, Texas, and Georgia all agreed to grant their electoral votes to whichever candidate gets the most total votes among all three states combined, then you'd have essentially a super-swing state with over 100 electoral votes, and it would be nearly impossible to win the election without winning those votes. You'd thus create a huge incentive for the candidates to spend most of their time campaigning in just those three states. Then other states would form their own compacts (or sign onto NPVIC) to retaliate.
